1. Field of the Invention
The present invention relates to the biological control of postharvest diseases in agricultural commodities. More particularly, this invention relates to the use of selected strains of microorganisms to biologically control postharvest diseases including mucor rot, gray mold, and blue mold in fruit.
2. Description of the Art
Fruit damage caused by fungi-induced postharvest diseases results in considerable economic losses to the fruit industry worldwide. Some of the most important postharvest diseases of fruit are mucor rot, caused by mucor spp., blue mold caused by Penicillium expansum, and gray mold caused by Botrytis cinerea.
Mucor spp., primarily Mucor piriformis, the causal fungus of mucor rot, survives in the soil and on rotting fruit in contact with the soil. During harvest, fruit are placed into large wooden bins which rest on the ground. During handling and loading, orchard soil, carrying spores of the fungus, adheres to the bin skids. Fruit become inoculated with the fungus when the bins, along with adhering soil, are placed in immersion dumpers in fruit packinghouses to float the fruit out of the bins and into the processing flumes, and the soil carrying the spores is released into the flume or dumper water. When the spores enter wounds in the fruit they germinate and grow. During growth, the fungus secretes enzymes that break down the fruit tissues, causing them to become soft, watery, and discolored. Currently, there are no postharvest fungicides that give control of this fungus.
Gray mold and blue mold are also major postharvest diseases of fruit and are primarily storage diseases. Traditional attempts to control postharvest diseases include the treatment of the commodity, after harvest and before storage, with a fungicide, for example, benomyl. However, increasing numbers of fungicide-tolerant strains of pathogens associated with postharvest diseases, as well as public concern about pesticide residues on food products,has stimulated efforts to develop alternative systems of disease control for agricultural products. In the case of mucor rot, a further incentive is that no chemical control treatment is available, because fungicides, e.g., benomyl, do not affect Mucor spp.
One alternative is the use of biological agents to control postharvest diseases. Postharvest biological control systems for fruit have been actively investigated for the past decade. These include iturins as antifungal peptides in biological control of peach brown rot with Bacillus subtilis (C. G. Gueldner et al., Journal of Agricultural and Food Chemistry 36: 366-370 (1988)); postharvest control of blue mold on apples using Pseudomonas spp. isolate L-22-64 or white yeast isolate F-43-31 (W. J. Janisiewicz, Phytopathology 77: 481-485 (1987)); biocontrol of blue mold and gray mold on apples using an antagonistic mixture of Pseudomonas sp. and Acremonium breve (W. J. Janisiewicz, Phytopathology 78: 194-198 (1988)); control of gray mold and reduction in blue mold on apples and pears with an isolate of Pseudomonas capacia and pyrrolnitrin produced therefrom (W. J. Janisiewicz and J. Roitman, Phytopathology 78: 1697-1700 (1988)); postharvest control of brown rot in peaches and other stone fruit with the B-3 strain of Bacillus subtilis (P. L. Pusey and C. L. Wilson, Plant Disease 68: 753-756 (1984); P. L. Pusey et al., Plant Disease 70: 587-590 (1986), P. L. Pusey et al., Plant Disease 72: 622-626 (1988), and U.S. Pat. No. 4,764,371 to Pusey et al.); antagonistic action of Trichoderma pseudokoningii against Botrytis cinerea Pers. which causes the dry eye rot disease of apple (A. Tronsmo and J. Raa, Phytopath. Z. 89: 216-220 (1977)), and postharvest control of brown rot and alternaria rot in cherries by isolates of Bacillus subtilis and Enterobacter aerogenes (R. S. Utkhede and P. L. Sholberg, Canadian Journal of Microbiology 32: 963-967 (1986)). Presently, there are no postharvest biocontrol systems in widespread commercial use.